The invention relates to an agent for the gene therapy of tumor diseases and neurodegenerative, cardiovascular and autoimmune diseases. Areas of application for the invention are medicine and the pharmaceutical industry.
After bronchial carcinoma in men and breast tumors in women, tumors of the large intestine and the colon are the malignant tumors, which occur most frequently in Germany. For these patients, the essential therapeutic measure consists of the radical resection of the tumor-carrying section of the intestine. However, metastasizing (primarily liver metastasizing) is the main cause of the high mortality of colorectal carcinoma. When surgical treatment of the metastases no longer is possible, intensive chemotherapy generally remains the last means of choice.
In spite of intensive research of new potent chemotherapeutic agents, the treatment of tumors that cannot be resected, especially of liver metastases, continues to be a problem because colorectal carcinoma have a low cell proliferation rate, a tumor heterogeneity and a resistance to drugs. A different reason for the frequent failure of chemotherapy lies therein that the cytostatic agents, presently available, do not attack certain metabolic paths of tumors selectively nor are directed exclusively against tumor cells. Consequently, the use of cytostatic agents is associated with many severe side effects.
The use of liposomes and polymers offers the possibility of modifying the pharmacological properties of chemotherapeutic agents.
In spite of decades of intensive efforts to heal patients with inoperable tumors with the help of chemotherapy, progress must be described as slight. With the exception of a few diseases (such as acute lymphatic leukemia) complete healing of the patients by chemotherapeutic measures alone is not possible. In many cases, no significant increase in the life expectancy can be detected. This is due, on the one hand, to the slight tumor specificity of many chemotherapeutic agents and, on the other, to the relatively high toxicity of these substances. Consequently, in spite of massive side effects, an adequate activity level can be observed only rarely in the tumor. In 28 different studies, a total of 663 patients were treated with 22 different substances. Only six patients showed a complete tumor regression and 63 a temporary one which, however, in most cases did not lead to a significant prolongation in the survival time. These studies confirm clearly the need for improving existing therapy concepts and, optionally, for developing new starting points.
Because of their similarity to cell membranes, liposomes have been used for 23 years as multifunctional carrier and transporting systems for biologically active substances, including prokaryontic and eukaryontic genes (Kim, S., Drugs, 1993, 46: 618-638). They can be characterized as closed microscopic structures, which consist of concentrically disposed lipid double layers, which in turn separate aqueous compartments from one another. Particularly extensive is the work dealing with the liposomal encapsulation of medicinal drugs. In comparison to other carrier systems, the liposomes offer the advantage here that they can be utilized also for the encapsulation of DNA constructs.                The ability to select the composition, charge, size and stability, depending upon the problem that is to be solved.        The possibility of complete biological degradation.        The practical absence of immunological and toxic reactions.        The frequently changed pharmacokinetics of the liposomally encapsulated substance.        The changed organ distribution and tropism to certain organs.        The possibilities for different methods of targeting (antibodies, lectins)        
Liposomes can also be used as gene-transfer systems.
However, in the majority of animal experimental models, the gene transfer was carried out ex vivo. The knowledge concerning a tumor-specific immune response, induced by the gene-modified tumor cells and obtained by these means, has led to the strategy of a “vaccination” with cytokinin-gene transfected tumor cells. An in vivo gene transfer strategy was employed within the scope of an RAC-approved study at the University of Michigan Medical Center, Ann Arbor. The transfer of an MHC class I (HLA-B7) gene into the tumor cells was to be achieved by the direct injection of liposomes/plasmid DNA complexes into the tumor tissue, in order to stimulate an immune reaction by these means. Other gene transfer systems make use of suicides genes, in order to make tumor cells sensitive to chemotherapeutic substances. Different genes, which can cause a selective killing of the expressed cells, have been tested for this purpose.
A simple and, according to first clinical data, also effective system was developed by K. Culver (Culver, K. W. et al., Science 1992, 256: 1550) and has already been employed in clinical studies. The strategy is based on the transfer of the herpes simplex thymidine kinase (HSV-tk) gene into tumor cells by means of a retroviral vector. HSV-tk-transfected cells become sensitive to the anti-virus substance ganciclovir. Due to HSV-tk, ganciclovir becomes a nucleotide-like precursor which, after further phosphorylization, is incorporated into the DNA-dividing cells and leads to a stop in the symphysis of DNA and to the death of the cell.
By means of an adaptation of the Culver suicide strategy to the liver metastasis model and after injection of HSV-tk vector-producing cells, Caruso et al. (Proc. natl. Acad. Sci., 1993, 90: 7024-7028) was able to confirm a regression of established, macroscopically visible liver metastases. However, it is a disadvantage of this application of a tumor therapy with viral vectors that, because of the immunological defense mechanism of the organism, only a single administration of the gene vector construct is possible. For a liposomal vector, repeated systemic processing is possible.
For the treatment of tumors, the access to which is relatively difficult (such as multiple liver metastases, brain tumors), the selective and safe application and transfection with retroviral or adenoviral vectors still is a problem, quite apart from the treatment risks, which occur with viral infections. As little as possible of healthy tissue should be destroyed and involved, while the transfer efficiency is as high as possible and the subsequent tumor regression is complete.
Until now, no liposomally packaged therapy gene or suicide gene has been transfected in liver metastases at the CC531 carcinoma.